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The sweating illness was one of the most horrifying diseases of the 15th and 16th centuries and even more mysterious than the Black Death.

It seemed to come from out of nowhere and yet death came mercilessly fast.

It started with a feeling of being freezing cold, the body convulsing in uncontrollable shivering, with severe prostration, heart palpitations, extreme aches in the neck, dizziness, dehydration and headaches, often with a vesicular rash.

Then came the worst part — violent, drenching sweating, along with delirium, and a rapid pulse. Between 30-50 per cent of victims were dead just three to 18 hours later.

And yet, if you were lucky enough to last 24 hours, you had a good chance of a full recovery.

The strange illness still fascinates scientists today because nobody knows for sure how the disease managed to rip through Europe several times during the tumultuous Tudor period.

The epidemic's origins and even the identity of the disease are still unknown, apart from the fact that the patient literally sweated to death.

It was 534 years ago that the sweating illness, known as "The Sweat" tore through England, leaving thousands of people healthy one day and dead the next.

SWEATING TO DEATH

So much about the Sweat was puzzling, including the notion that surviving the disease didn't make you immune from another attack; it was common for patients to be struck by the frightening disease several times.

English physician Dr John Caius (also known as Johannes Caius) was working in Shrewsbury, England in 1551 when an outbreak of the sweating sickness had a stranglehold over the terrified townsfolk.

Caius became something of a celebrity when he wrote an account of the disease which is the main historical source of knowledge of the sickness.

While nobody knew exactly what caused the Sweat, Caius believed it was linked to dirt and, because the illness broke out in late spring or summer, that it was also linked to insects.

Caius was treating many wealthy patients and his manuscript details his observations of the symptoms, as well as ideas for prevention and cure. While advising people to avoid "evil mists and rotten fruit" might sound odd today, it's a reflection on where medical knowledge was in 16th Century.

Caius wrote: "This disease is not a Sweat only (as it is thought and called), but a fever … in the spirits by putrefaction venomous. First by the pain in the back or shoulder, pain in the extreme parts, as arm, or leg. Secondly by the grief in the liver and stomach. Thirdly by the pain in the head, & madness. Fourthly by the passion of the heart.

"Whereupon also follows a heaviness, (the fifth token of this disease), and a desire to sleep, never contented, the senses in all parts being as they were bound or closed up. Last follows the short abidings, a certain token of the disease."

He also advised people to exercise frequently and that, in the early stages of the illness, one must drink herbal mixtures and avoid being outside.

Dr John Caius. Photo / Supplied

WHERE DID THE SWEAT COME FROM?

It's not clear who first contracted sweating sickness, but there's a theory held by some historians that the disease came to England via a group of French soldiers King Henry VII's father had hired to secure the throne for him and his son in 1487 and end the Wars of the Roses.

Whether the mercenaries actually brought sweating sickness to England will never be known but one theory is that the illness was first heard of at the Battle of Bosworth, and then followed the King's men back to London where 15,000 people died from the disease in six weeks.

There were five known epidemics of the Sweat — in 1485, 1508, 1517, 1528, and 1551.

While the disease was mostly contained in England, the outbreak in 1528 managed to kill 2,000 in London before the sickness travelled via passengers on a ship to Hamburg, Germany, where more than a thousand deaths occurred in four weeks.

A further 3,000 people died in Danzig and Lübeck before the illness spread to Scandinavia, Denmark and Russia. The disease managed to totally bypass Italy and most of France (apart from Calais in the north.)

King Henry's printer Richard Grafton referred to the sweating sickness as a new kind of sickness. Grafton wrote of the illness: "So sore, so painful, and sharp, that the like was never heard of to any man's remembrance before that time."

It says a lot about the severity of the Sweat when you consider that the people who've written about how horrendous it was, were people that had also seen the horrors of the Black Death.

But while the Sweat was undoubtedly frightening, it wasn't quite as devastating as the Black Death, in terms of mortality rates.

The bubonic plague swept across England between 1346 and 1353, killing more than 20 million people (about 60 per cent of the population). One factor that set the Sweat apart from the Black Death was that the former was puzzling from beginning to end while the mystery of the bubonic plague was solved when it was discovered to be spread by infected fleas from small animals, such as rats.

KING HENRY VIII WAS PARANOID ABOUT CATCHING THE SWEAT

According to author Alison Weir, King Henry VIII was said to be terrified of the Sweat and he demanded to be moved around England in a bid to escape the spread of the disease.

The King had good reason to be scared, as the disease was spreading like wildfire and seemed to be favouring the well-to-do. Weir writes that King Henry fled London with his Queen and a group of people, including his mistress Anne Boleyn.

"In June 1528 the sweating sickness returned to plague London and, later on, the rest of the country. This was a particularly virulent outbreak and the King, learning with horror that some members of his household had succumbed to the disease fled to another house and then another after that, until he was sleeping in a different place each night."

King Henry VIII was so terrified of the disease he demanded to be moved around England in order to escape it. Photo / Supplied

THE WORST EPIDEMIC

In 1485 physician Thomas Forrestier wrote several accounts of the Sweat after witnessing his patients succumb to the illness and also this account of simply being out in the streets at the time of the epidemic.

"We saw two priests standing together and speaking together, and saw both of them die suddenly. Also we saw the wife of a tailor suddenly die. Another young man walking by the street fell down suddenly. Also another gentleman riding out of the city died. Also many other which were to rehearse we have known that have died suddenly."

Arthur Prince of Wales (Henry VIII's brother) is thought to have suffered from the sweating sickness. Photo / Supplied

MORE THEORIES

The jury is still out on what caused the Sweat. Some modern researchers have proposed that it was caused by the hantavirus infection which is transmitted by certain mice, rats, and voles. The symptoms of the Sweat are said to be similar to hantavirus pulmonary syndrome.

Other scientists believe anthrax might have been the cause: during the bioterrorism attacks of 2001 that resulted in five deaths, one of the major symptoms was copious sweating. Others believe the Sweat might have been a version of the flu or a sickness known as 'relapsing fever'. Whatever its origins, the Sweat carried the same kind of terror that the Ebola virus carried today.

Henry Brandon, Duke of Suffolk, died during the Sweat epidemic of 1551 — his body was buried in a cemetery that still exists. While it's possible to exhume his remains and search for hantavirus, scientists say it's unlikely the genetic material has survived and so there are no immediate plans to disturb the Duke's remains.

Henry Brandon reportedly died of the sweating sickness in 1551. Photo / Supplied

THE END OF THE SCOURGE

In 1551 the Sweat stopped as suddenly as it began. A similar illness known as the "Picardy Sweat" occurred 150 years later in France, but that sickness came and went very quickly, making it virtually impossible for scientists to compare the two 'sweaty' diseases.

Also, thanks to slack record keeping, nobody really knows exactly how many people died from the Sweat although clearly thousands lost their lives. All historians have to rely on is scattered, vague health records and personal diaries.

And while Anne Boleyn didn't manage to survive her marriage to King Henry VIII, she was rumoured to have contracted the dreaded sweating sickness and come out of the scourge alive.